Rainier Therapeutics Expands Leadership Team to Prepare for Late-Stage Clinical Trials

SAN LEANDRO, Calif., January 3, 2019

— Rainier Therapeutics, Inc., a privately-held clinical
stage drug development company focused on helping patients in the high unmet need area of
bladder cancer, today announced the expansion of its team with appointments spanning
regulatory, medical affairs, corporate development and legal affairs, as well as
pharmacovigilance.

Recent additions to the Rainier Therapeutics team include Valerie Fauvelle, Vice President,
Regulatory Affairs; Florian D. Vogl, MD, PhD, MSc, Senior Medical Director, Europe; Max
Barker, Vice President, Corporate Development and Legal Affairs; and David Yong, PharmD,
Senior Director, Drug Safety.

“We are pleased to announce the continued build-out of our team with the addition of these
experienced personnel, who collectively will guide the planned advancement of vofatamab (B701) for metastatic and non-metastatic bladder cancer,” said Scott D. Myers, Chairman and
Chief Executive Officer of Rainier Therapeutics.

Valerie Fauvelle brings more than 18 years of regulatory affairs experience in drug
development to Rainier Therapeutics, most recently serving as Senior Director, Regulatory
Affairs at Cascadian Therapeutics. Prior to Cascadian Therapeutics, she held positions with
Gilead Sciences, ICOS, and Seattle Genetics.

Dr. Vogl joins Rainier Therapeutics from Novartis, where he served as Senior Global Medical
Leader, Oncology Development, providing leadership of the clinical development plan from
translational research through to late development. Prior to Novartis, Dr. Vogl served as Early
Development Leader, Oncology Pipeline at Amgen.

Max Barker joins the company from Cascadian Therapeutics, where he most recently served
as the company’s Vice President of Legal Affairs and Associate General Counsel. Mr. Barker
supported the expansion of the company’s lead program into a global, pivotal study and
supported the successful sale of Cascadian Therapeutics to Seattle Genetics in March 2018.
Previously, Mr. Barker was General Counsel and Vice President of Finance at Polaris
Pharmaceuticals, a multinational biotechnology company, leading legal, financial and
administration activities for Polaris and its subsidiaries. Prior to that, Mr. Barker was an
associate in the corporate practices of Cooley LLP and DLA Piper LLP in San Diego. Mr.
Barker received his Juris Doctorate from The University of Chicago Law School.

Dr. Yong brings more than 19 years of drug safety and pharmacovigilance experience to
Rainier Therapeutics, most recently serving as Associate Director, Clinical Drug Safety at
Cascadian Therapeutics with primary responsibilities in pharmacovigilance, signal detection
and serious adverse event processing. Prior to Cascadian Therapeutics, Dr. Yong held
positions with Onyx Pharmaceuticals (which was acquired by Amgen), Allos Therapeutics, OSI
Pharmaceuticals and Pathogenesis Corporation.
About Rainier Therapeutics

Rainier Therapeutics, Inc. is a privately-held, clinical stage biotechnology company developing
a targeted biologic for the potential treatment of metastatic and early stage bladder cancer, an
area of high unmet medical need. The company’s antibody, vofatamab (B-701) is focused
specifically on the fibroblast growth factor receptor 3 (FGFR3), a known driver of bladder and
other cancers. Vofatamab is the most advanced targeted biologic specific for FGFR3 known by
Rainier to be in clinical development.

Rainier Therapeutics has ongoing Phase 1b and Phase 2 clinical studies of vofatamab in
metastatic bladder cancer – the Fierce 21 and Fierce 22 studies. In addition, Rainier
Therapeutics plans to study vofatamab in early stage bladder cancer – the Fierce 23 trial.
The Fierce 21 trial is evaluating vofatamab alone and in combination with docetaxel versus
docetaxel alone to determine safety and efficacy in the treatment of patients with locally
advanced or metastatic bladder cancer with FGFR3 mutant/fusion who have relapsed after, or
are refractory to, at least one prior line of chemotherapy. For more on this trial, visit
www.clinicaltrials.gov (NCT0240542).
The Fierce 22 trial is evaluating vofatamab in combination with pembrolizumab, an immune
checkpoint inhibitor, to determine safety, tolerability and efficacy in the treatment of patients
with locally advanced or metastatic bladder cancer, who have progressed following platinumbased chemotherapy and who have not received prior immune checkpoint inhibitor therapy.

For more on this trial, visit www.clinicaltrials.gov (NCT03123055).
The Fierce 23 trial will evaluate vofatamab monotherapy in non-muscle invasive bladder
cancer (NMIBC). This trial is planned to start in 2019.

Rainier Therapeutics’ website is: www.rainierrx.com.

Contacts:
Rainier Therapeutics
Julie Eastland
Chief Financial and Business Officer
Rainier Therapeutics, Inc.
(206) 718-0223
info@rainierrx.com

Laurence Watts
Westwicke Partners, LLC
Corporate Communications
(858) 356-5930
laurence.watts@westwicke.com

Julie Rathbun
Rathbun Communications
(206) 769-9291
media@rainierrx.com